This invention relates to magnetic flowmeters used for water, chemical or wastewater process pipes. In particular, this invention relates to detecting low liquid conductivity or empty pipe conditions in these magnetic flowmeters.
The calibration or accuracy of the flow rate output of a magnetic flowmeter can be compromised if there is low conductivity in the electrode circuit of the magnetic flowmeter. Low conductivity in the electrode circuit is often an indication of problems such as a partially filled or empty pipe, low liquid conductivity, fouled or polarized electrodes, or a broken or disconnected electrode lead.
Various conductivity circuits are known that generate and inject ac, dc or pulsed signal into the electrode circuit to detect conductivity. This injection creates an undesired path for current leakage of a portion of the flow signal back through the conductivity circuit. A calibration shift or inaccuracy of the flow rate output results from this leakage.
There is a need for a conduction indication that avoids these current leakage problems.
A magnetic flowmeter is disclosed that has an improved liquid conduction indication. The conduction indication uses naturally occurring xe2x80x9cramp pulsesxe2x80x9d which are related to conductance of the liquid are found in an electrode circuit of the magnetic flowmeter. These ramp pulses are used as a liquid conduction indication.
The conduction indication does not require electrically connecting any drive or excitation circuit to the electrode circuit, and loading of the electrode circuit can be avoided.